1. Field of the Invention
The invention relates generally to chilled water comfort cooling and industrial process cooling systems and in particular to methods and apparatus for efficiently operating chilled water cooling systems.
2. Related Art
Many commercial and other buildings and campuses are cooled by chilled water plants. In general, these chilled water plants produce chilled water which is pumped to air handlers to cool building air. Chillers, air handlers, and other components of a chilled water plant are designed to operate at a specific chilled water entering and leaving temperature, or Delta T. At design Delta T, these components are at their most efficient and can produce cooling output at their rated capacity. Low Delta T, which occurs when the entering and leaving temperature become closer than the design Delta T, reduces efficiency and cooling capacity of the chilled water plant and causes the chilled water plant to use more energy than required for a given demand.
Chilled water plants are designed to meet a maximum possible cooling demand of a building, campus, or the like, also known as the design condition. At the design condition, chilled water plant components are at the upper end of their capacity, where the system is most energy efficient. However, it is rare that such a high demand for cooling is necessary. In fact, almost all chilled water plants operate below design conditions for 90% of the year. For example, cool weather conditions can cause cooling demand to drop considerably. As cooling demand is reduced, Delta T is often also reduced. This means that for the majority of the time, almost all chilled water plants are operating at low Delta T and less than optimal efficiency. This chronic low Delta T, is referred to as Low Delta T Syndrome.
Many mitigation strategies have been developed to address Low Delta T Syndrome, such as through the use of sophisticated sequencing programs and equipment ON/OFF selection algorithms, but none have proven to completely resolve this phenomenon. In most instances, the chilled water plant operator simply pumps more water to system air handlers to increase their output, but this has the compounding effect of further reducing the already low Delta T. Also, increased pumping in the secondary loop results in higher than necessary pumping energy usage.
From the discussion that follows, it will become apparent that the present invention addresses the deficiencies associated with the prior art while providing numerous additional advantages and benefits not contemplated or possible with prior art constructions.